But the ACT Government wants to go further and give full marriage equality to same-sex couples.

The Federal Government argues it has the sole responsibility for marriage laws, but ACT Attorney-General Simon Corbell says he is confident the Territory has the authority to go further.

"We have clear legal advice that such a scheme is possible, constitutionally in the ACT, to provide same-sex couples the highest level of equality," he said.

"The Commonwealth Marriage Act has been constructed as being exclusively between a man and a woman, any other marriage that engages for example same-sex couples is not captured by the Commonwealth mandate.

"So that's the legal opinion that we have very clearly put to us."

Last week a New South Wales Parliamentary inquiry found the state has the power to legislate for same-sex marriage.

Mr Corbell says the ACT could be the first jurisdiction to pass such legislation.

"There is a clear majority on the floor of the Legislative Assembly that would support such as scheme, and we have a clear legal power to legislate in this space," he said.

"We will be proceeding with the preparation and introduction of that legislation to give same-sex couples legal recognition and legal equality when it comes to the recognition of their relationship."

Progressing marriage equality in the Territory is part of the Parliamentary Agreement between ACT Labor and Greens MLA Shane Rattenbury.

Mr Rattenbury says he is hopeful the legislation will pass.

"The important part is getting the details right," he said.

"That very fine detail will be quite important, particularly given the potential for legal challenges down the line which certainly some in the community have flagged they may undertake."

Free trade is the oldest argument in federal politics and the issue that literally defined the federation era but opposition exists to the TPP, courtesy of the Investor-State Dispute Resolutions clause.